Conventionally, in a manufacturing process of a magnetic disk apparatus, servo track writer equipment sets a track recording density TPI, i.e., track pitches by which a required recording capacity can be obtained on a magnetic disk medium to write servo tracks. When the servo tracks are to be written, the track pitches have to be determined according to the write core width of a head so that adjacent tracks are not erased; however, in addition to that, in consideration of pitch errors between the tracks upon servo track write, they are determined so that the track pitches tend to be wide. Moreover, in a conventional processing process of servo track write, as an examination in the process, whether read/write can be correctly performed on the tracks per se is examined.
Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2003-331545
Meanwhile, recently, the more the track density is increased along with miniaturization of a write core and a read core, the more the track pitches are narrowed; therefore, the influence of variations which are generated when the servo tracks are written in the servo track writer equipment becomes large.
However, although the tracks per se are examined as the examination in the process such as that of defects (medium defects), the track pitches are not examined; therefore, it may pass and be shipped with remaining narrow track pitches. In such a magnetic disk apparatus, the narrow tracks may be written over by write of adjacent tracks after shipment, and the written data may become unreadable.
Meanwhile, there is a method which measures write/erase margins as a method of examining the influence of write of adjacent tracks. In the write/erase margins, after test data is written to an objective track, different test data is written to an adjacent track, the objective track is read, and, when the read can be performed, the adjacent track is written so that the objective track is narrowed, thereby measuring the writing limit through narrowing by the adjacent track. However, in the measurement of the write/erase margin, the error rate of the objective track is obtained while performing the narrowing write of the adjacent track, and measurement of one track takes considerable time. Therefore, there is a problem that it cannot be applied to examination of abnormality, in which the track pitches are narrow, with respect to the entire surface of the magnetic disk medium since productivity is significantly impaired.